This invention relates to an apparatus for examination and treating an eye, having optical means including an illumination tube for illumination of the eye, a laser beam source and means for optically coupling the laser beam into said optical illuminating means for laser coagulation. Apparatus of this type, particularly slit lamps are well known in the art.
One of the known embodiments has a semi-transparent mirror in its illumination tube, the illumination light passing through this mirror and the entering laser beam being reflected into the axis of the illumination optic by said semi-transparent mirror (DE-A-2611933). While this prior apparatus is simple it involves substantial light losses as well for the illumination as for the laser beam.
In order to avoid at least a part of these drawbacks it has also been known to provide a pair of prisms immediately after the condenser in the illumination tube, these prisms spiting the illumination rays into two lateral partial rays passing at the side of the mirror provided for coupling the laser beam into the illumination optic. The laser beam and both partial beams of illumination rays are reflected into the eye by separate mirrors (EP-A-0225699). However, this embodiment also has various drawbacks. It needs a special design of the illumination tube with additional prisms, and this illumination tube has to have a larger diameter. Therefore, it is not possible to use the illumination tube of an existing diagnostic slit lamp. Rotation of the slit diaphragm and of the whole illumination tube respectively together with the slit diaphragm which is generally usual and desirable now a days is not possible or is only possible to a limited degree because with larger rotation by up to 90.degree. no light would reach the eye over the reflecting mirror.